Cavity forming device and method of constructing a cavity wall

ABSTRACT

A cavity forming device, also referred to as a cavity forming retaining clip, includes a first face and a second face. The first face and the second face are connected together by a body. The body is elongate and extends along an imaginary longitudinal axis from the first face to the second face. The body separates the first face from the second face by a predetermined distance. The second face is arranged to receive a wall therethrough. In use a backing board for an outer skin is able to be clamped against the cavity forming device.

BACKGROUND

1. Technical Field

The invention relates to a cavity forming device and in particular, but not exclusively, a cavity forming device for a cavity wall. The invention also relates to a method of constructing a cavity wall.

2. Description of Related Art

Cavity walls normally comprise two skins separated by a hollow space, or cavity. One of the skins is arranged to be on the outer-side of the wall, and is often called an outer skin. The other of the skins is arranged on the inside of the wall, and is often called an inner skin.

Outer skins are commonly constructed from stone, brick or concrete block. Inner skins are commonly constructed from concrete block or timber-cladding.

Stone, brick and concrete block are all absorbent materials and therefore tend to draw moisture, such as rainwater or water vapour from the atmosphere, into the outer skin. Eventually, the moisture is drawn to the inner-side of the outer skin where, under normal circumstances, the moisture runs down the inner-surface of the outer skin to drain into the ground or through weep holes in the base of the cavity wall. It is important that the moisture does not reach the inner skin so that the cavity can effectively work as a moisture barrier, preventing the inner skin from becoming damp.

Wall ties are commonly used to connect the outer and inner skins to tie the two skins together to spread loads acting on the wall. Wall ties are specifically designed to prevent moisture bridging from the outer skin to the inner skin. However, mortar droppings may fall into the cavity during construction and may bridge the cavity, for example by resting on the wall ties or collecting at the base of the cavity. The mortar droppings can prevent the cavity acting as a moisture barrier.

Granted Patent GB 2 388 614, published in 2004, provides a spacer device to prevent mortar bridging as shown in FIG. 10 of this application (which corresponds to FIG. 3 of GB 2 388 614).

Referring to FIG. 10, the spacer device 11 is integrally formed having a support body 12 with a plurality of projections 13 extending transversely from the plane of the support body 12. The support body 12 is a laminar sheet having dimensions of 1200 mm by 450 mm and a depth of 8 mm. The support body 12 and the projections 13 of the spacer device 11 are made from polypropylene. The plurality of projections 13 are longitudinal and have a proximal end 14 located adjacent to an inner face of the support body 12 and a distal end 15 located away from the support body 12. Each of the projections 13 of the support body 12 is spaced from one another by a distance of 100 mm. The projections 13 have a circular cylindrical shape. A ridge or rib 16 is formed in each projection 13 at a point equidistant between the proximal and distal ends 14, 15 of the projection 13. The ribs 16 extend entirely circumferentially about the projections 13.

The spacer device 11 is incorporated in a cavity 17 of a cavity wall 18 of a building structure. The cavity wall 18 has an exterior wall 19 and an interior wall 20 and may optionally include a layer 21 of an insulating material on an inner face of the interior wall 20. The exterior and interior walls 19, 20 are constructed from bricks, although the walls 19, 20 may also be constructed from concrete blocks, hollow clay bricks, timber framing or natural stone. The spacer device 11 is secured in the cavity 17 of the cavity wall 18 by an H-shaped connecting element 22. The support body 12 of the spacer device 11 lies against an inner face of the exterior wall 19 with the plurality of projections 13 extending toward an inner face of the interior wall 20. The ribs 16 located at mid-points along the projections serve to function as a “water bar” to prevent or hinder the penetration of water or moisture into the interior wall 20 of the building.

However, the spacer device 11 of FIG. 10 is relatively expensive to manufacture, bulky to transport and store, and awkward to install due to its size and the necessity for the H-shaped connecting element 22, which, itself may form a moisture bridge between the outer and inner skins 19, 20 respectively. The projections 13 can also fill with mortar to create cold bridging reducing the effectiveness of the cavity as a heat insulator.

An aim of the invention is to provide a cavity forming device and method of constructing a cavity wall which is at least one of a cheaper, smaller and easier to install solution, and which is potentially more reliable.

SUMMARY OF THE INVENTION

Broadly speaking, the invention provides a cavity forming device which is easily attachable onto existing wall ties and which may serve to create a cavity between inner and outer skins of a cavity wall. The cavity forming device is used in conjunction with a separate backing board for the outer skin. The backing board is clamped in place using the cavity forming device of the invention, a wall tie and wall tie retaining clip (both of which are currently available on the market).

This new configuration prevents mortar dropping from creating a moisture bridge between the outer skin and the inner skin in use in a cheap and easy-to-use way. Additionally, each cavity forming device is relatively small and relatively cheap to manufacture. Also, cold bridging may also be prevented. The backing board can be any suitable board already known for this purpose. However a more useful and surprising backing board is described later in this document.

According to one aspect of the invention, there is provided a cavity forming device for a cavity wall, the device comprising: a first face; a second face connected to the first face by a body to set a predetermined distance between the first face and the second face corresponding to a cavity depth in use; and wherein the second face is arranged to receive a wall tie therethrough.

In this way, a backing board for an outer skin is able to be clamped in place against the cavity forming device using the wall tie and a wall tie retaining clip. The cavity forming device is relatively lightweight and may be made relatively easy to stack and transport. The cavity forming device is relatively easy to install, being locatable on each wall tie in the construction process. The lack of projections open at one end will prevent cold bridging.

Preferably, the cavity forming device has means for securing the cavity forming device within the cavity wall. Preferably, the means for securing allows the cavity forming device to attach to a wall tie. Preferably, the cavity forming device has is a detent notch for attachment to a wall tie. Preferably, the detent notch is located on the second face. Alternatively, or additionally, the cavity forming device comprises a channel with abutment shoulders for attaching the device to a wall tie. Preferably, the channel is tapered and tapers outwardly toward the abutment shoulders. Alternatively, or additionally, the cavity forming device has a lug defining an aperture which is arranged adjacent the first face.

Preferably, the first face comprises a rim which extends outwardly from the body. Preferably, the first face forms a generally horse-shoe type circumferential rim defining an opening.

Preferably, the second face has an aperture for receiving the wall tie in use. Preferably, the aperture is a stepped channel having a first channel adjacent an edge of the second face which is wider than a second channel arranged across a longitudinal axis of the device. Preferably, the second channel comprises a notch. Preferably, the notch is substantially coaxial with the longitudinal axis of the device.

Preferably, the opening of the first face and the aperture of the second face generally coincide to receive a wall tie in use. Preferably, the first face and the second face are parallel.

Preferably, the body is generally cylindrical. In the exemplary embodiment, the body comprises a plurality of ribs. More particularly three or six ribs. Preferably, each rib is arranged to flex. In one embodiment, at least two ribs define an aperture approximately half-way between the first face and the second face. More preferably, the at least two ribs are closest the opening in the first face. Preferably, the at least two ribs widen to accommodate the aperture, thereby creating bowed sub-ribbed portions. In another embodiment, the ribs define body apertures which include at least one elongated circle.

Preferably, the body comprises a slot adjacent the first face. Preferably, the slot is arranged to be opposite the opening of the first face. Preferably, the slot is transverse to the longitudinal axis of the device.

Preferably, the predetermined distance between the first face and the second face is at least 25 mm. Preferably, the predetermined distance between the first face and the second face is between 25 mm and 200 mm. Preferably, the predetermined distance is between 50 mm and 100 mm. Most preferably, the predetermined distance is approximately 50 mm.

According to another aspect of the invention, there is provided a method of constructing a cavity wall, the method comprising:

a) building an inner skin to a predetermined height including attaching at least one wall tie;

b) securing a cavity forming device against the inner skin so that the cavity forming device receives the wall tie;

c) positioning an outer skin backing board against the cavity forming device;

d) securing the backing board against the cavity forming device using the wall tie;

e) building an outer skin to a predetermined height adjacent the backing board using the wall tie to secure the outer skin to the inner skin.

Preferably, the inner skin is constructed from masonry or block work, and the wall tie is laid between courses. Preferably, the cavity forming device is secured against the inner skin using the wall tie.

Alternatively, the inner skin is constructed from timber cladding, and the wall tie is attached to the timber cladding. Preferably, the cavity forming device is secured against the inner skin by direct attachment to the timber-cladding or the wall tie. Preferably, the direct attachment to the timber-cladding uses a nail. More preferably, the wall tie and the cavity forming device are secured to the timber cladding by the same means. Preferably, the direct attachment to the wall tie uses abutment shoulders in a tapered slot on a face of the cavity forming device.

Preferably, the backing board is secured against the cavity forming device using a wall tie retaining clip.

According to another aspect of the invention, there is provided the use of corrugated polypropylene board as a backing board in the construction of a cavity wall.

According to another aspect of the invention, there is provided a cavity wall comprising: an inner skin including at least one wall tie, a cavity forming device arranged against the inner skin so that the cavity forming device receives the wall tie, an outer skin backing board held against the cavity forming device; a wall tie retaining clip attached to the wall tie to hold the backing board against the cavity forming device; and an outer skin adjacent the outer skin backing board.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show how example embodiments may be carried into effect, reference will now be made to the accompanying drawings in which:

FIG. 1 is a perspective view of a cavity forming device in accordance with a first embodiment of the invention;

FIG. 2 is a side view of the cavity forming device of FIG. 1 shown together with a timber frame wall tie attached to a timber-clad cavity wall;

FIG. 3 is a side view of the timber-clad cavity wall device of FIG. 1, the device being in position in a timber-clad cavity wall and being shown in section;

FIG. 4 is a side view of the masonry cavity wall device of FIG. 1, the device being in position in a masonry cavity wall and being shown in section;

FIG. 5 is a plan view of a cavity forming device in accordance with a second embodiment of the invention;

FIG. 6 is a perspective rear view of the cavity forming device of FIG. 5;

FIG. 7 is a front view of the cavity forming device of FIG. 5;

FIG. 8 is a side view of a timber-clad cavity wall having the cavity forming device of FIG. 5 installed therein, and being shown in section;

FIG. 9 is a flow chart illustrating a method of constructing a cavity wall in accordance with another aspect of the invention; and

FIG. 10 is a prior art spacer device.

DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS

A cavity forming device 100 according to a first exemplary embodiment of the invention is now described with reference to FIGS. 1 to 4.

FIG. 1 is a perspective view of the cavity forming device 100. The cavity forming device 100, also referred to as a cavity forming retaining clip, comprises a first face 110 and a second face 120. The first face 110 and the second face 120 are connected together by a body 130. The body 130 is elongate and extends along an imaginary longitudinal axis from the first face 110 to the second face 120. The body 130 separates the first face 110 from the second face 120 by a predetermined distance. In this example, the predetermined distance is 50 mm.

In more detail, the first face 110 comprises a generally horse-shoe shaped rim 114 extending radially outwardly from the body 130. The horse-shoe shaped rim 114 defines an opening 116. The first face 110 also has three lugs 112 protruding outwardly from the rim 114. The lugs 112 are spaced evenly apart around the circumference of the first face 110. Each lug 112 defines a lug opening 113. Triangular-shaped reinforcement parts 140 are positioned between the first face 110 and the body 130.

The second face 120 is generally circular and extends inwardly from the body 130. The second face 120 defines an aperture 121. The aperture 121 comprises an outer channel 124 for receiving a timber frame wall tie. The outer channel 124 extends in a radial direction inwardly from an outer circumference of the second face 120 towards the longitudinal axis. The outer channel 124 is open at the outer circumference of the second face 120 and body 130. Before reaching the longitudinal axis, the outer channel 124 is stepped to a second, inner channel 125 being of narrower width than the outer channel 125. The stepping provides abutment shoulders 126 against which a timber frame wall tie can rest in use. The inner channel 125 is slightly narrower than a general purpose wall tie suitable for masonry walls. The inner channel 125 extends beyond the longitudinal axis in the same direction as the first channel 124 and ends before the outer circumference of the second face 120. The inner channel 125 defines a detent notch 122 at the intersection with the longitudinal axis which is arranged to receive and hold a general purpose wall tie. Cut away portions 118 are provided on the second face 120.

The body 130 comprises three ribs 132 each extending from the first face 110 to the second face 120. A first rib 132 is arranged opposite the opening 116 in the first face 110. Two other ribs 132 are arranged at approximately 120 degree intervals from the first rib. The ribs 132 lie on the circumference of an imaginary cylinder extending from the first face 110 to the second face 120. Each rib defines a rib aperture 134 approximately half-way between the first face 110 and the second face 120. Each rib aperture 134 is substantially circular. At the rib aperture 134, each rib widens to accommodate the rib aperture 134. By widening to accommodate the rib aperture 134, each rib 132 creates bowed sub-rib portions 136 which allow the cavity forming device 100 to flex. Also, the bowed sub-rib portions 136 act as moisture barriers to prevent moisture access from an outer skin to an inner skin of a cavity wall. In practice, water moving along the ribs 132 will collect at the lower-most bowed sub-rib portion 136 and will drip downwardly before reaching one of the first face 110 and the second face 120. The first rib comprises a slot 138 adjacent the first face 110. The slot 138 extends laterally in relation to the longitudinal axis.

The opening 116 of the first face is aligned with the outer channel 124 of the second face 120. The opening 116 is wider than the outer channel 124. Together, the opening 116 and the outer channel 124 allow a wall tie to pass into the cavity forming device 100 and to pass through at least the second face 120.

FIG. 2 is a side view of the cavity forming device 100 shown attached to an inner skin 161 of a cavity wall 160.

The cavity forming device 100 is shown together with a timber frame wall tie 150 which, as can be seen, passes through the outer channel 124 to rest against the abutment shoulders 126. In this example, the timber frame wall tie 150 passes through the slot 138 in the body 130 so that the timber frame wall tie 150 is positioned adjacent one of the lugs 112, which is arranged aligned with the first rib 132. A brad nail 151 is shown passing through the timber frame wall tie 150 and the lug opening 113 into the inner skin 161, which in this case is a timber frame, of the cavity wall 160.

FIG. 3 is a side view in cross section of a timber-clad cavity wall including the cavity forming device 100 of the invention.

The cavity wall 160 comprises an inner skin 161 including battens 162 and a plywood covering 163. The cavity forming device 100 and a corresponding timber frame wall tie 150 is shown attached to the plywood covering 163 by the brad nail 151. The timber frame wall tie 150 passes through the second face 120 of the cavity forming device 100. The device 100 rests on the abutment shoulders 126. The cavity wall 160 also comprises an outer skin 164 comprising a backing board 165 and several courses of natural stone 166. The timber frame wall tie 150 passes through the cavity forming device 100 and over a top surface of the backing board 165. A wall tie retaining clip 168 is positioned on the timber frame wall tie 150 to hold the backing board 165 against the cavity forming device 100. The protruding part of the timber frame wall tie 150 is embedded into a mortar layer between courses of the natural stone 166.

FIG. 4 shows a masonry cavity wall 160 having an inner skin 161 and an outer skin 164.

The inner skin 161 in this example comprises courses of concrete blocks 167 faced on the cavity side by insulation panels 168. A masonry, or general purpose, wall tie 152 is provided between courses of the block work 167, ideally between every other course. The insulation panels 168 are placed adjacent the protruding masonry wall tie 152, and the cavity forming device 100 is placed over the masonry wall tie 152 and is held in place by the notch 122 on the inner channel 125 of the second face 120 of the cavity forming device 100. The cavity wall 160 also comprises an outer skin 164 comprising a backing board 165 and several courses of natural stone 166. The backing board 165 abuts the second face 120 and a wall tie retaining clip 168 is used to keep the backing board 165 in place. The protruding part of the general purpose wall tie 152 is embedded into a mortar layer between courses of the natural stone 166.

Cavity walls are commonly specified to have a cavity depth of 100 mm. This includes any insulation panels 168 if any, and so often an open cavity is 50 mm deep where 50 mm insulation panels 168 are used.

Another cavity forming device 100 according to a second exemplary embodiment of the invention is now described with reference to FIGS. 5 to 8.

The cavity forming device 100 of the second exemplary embodiment is very similar to that described according to the first exemplary embodiment above with reference to FIGS. 1 to 4. Like reference numerals are used to refer to like components, and only the differences shall be described.

FIG. 5 is a plan view of the cavity forming device 100 of the second exemplary embodiment. Here, it can be seen that the configuration of the ribs 132 has changed. There are now six ribs 132 between the first face 110 and the second face 120. There are no rib apertures 134 in the second embodiment, nor are there bowed sub-rib portions 136. Instead, the ribs are generally elongate and solid and flare outwardly at each of the first face 110 and the second face 120. The ribs define five body apertures 139 around the body 130 of the cavity forming device 100. In this exemplary embodiment, two configurations of body apertures 139 are shown. The first configuration is in the form of an elongated circle. The second configuration is a circle which is larger than the elongated circle. Starting at the opening 116 of the first face 110, there are two elongated circles, one each adjacent the opening 116. Moving around the body 130, the elongated circles are each followed by the second configuration of body aperture 139, that is a larger circle. Finally the two larger circles each are adjacent a single elongated circle which is positioned approximately opposite the opening 116.

In this way, the cavity forming device 100 remains flexible and is able to flex under pressure. Moisture bridging is prevented by the shape of the body apertures 139 and ribs 132. The cavity forming device 100 is also considered to be stronger and easier to make.

FIG. 6 is a perspective rear view of the cavity forming device 100. Here, we focus on changes made to the second face 120, and in particular the outer channel 124 and abutment shoulders 126.

Firstly, it should be noted that an inward extension 128 is provided on the second face 120. The inward extension 128 extends inwardly into the body 130 of the cavity forming device 100. The purpose of the inward extension 128 is to deepen the abutment shoulders 126 so that greater contact with a timber frame wall tie 150 can be achieved in use. In this embodiment, the inward extension 128 extends inwardly by approximately 10 mm although an alternative extension of between about 5 and 15 mm would be useful.

Also, as can be seen in FIG. 6, the abutment shoulders 126 are arranged at an angle with respect to an imaginary longitudinal axis passing through the cavity forming device 100 from the first face 110 to the second face 120. In this exemplary embodiment, the abutment shoulders are angled so that the abutment shoulders 126 rise inwardly into the body 130, assuming here that the aperture 121 of the outer channel 124 defines a bottom of the cavity forming device 100.

It should also be noted that the detent notch 122 for receiving a general purpose wall tie 152 has been moved away from a longitudinal axis of the cavity forming device 100, and in particular away from the aperture 121 of the outer channel 124. In this second exemplary embodiment of the invention, the detent notch 122 and the abutment shoulders 126 are approximately evenly spaced around the longitudinal axis as it passes through the second face 120.

Referring now to FIG. 7 which is a front view of the cavity forming device 100 according to the second exemplary embodiment, we see that the outer channel 124 tapers radially on the second face 120. In particular, the outer channel 124 is broader at the abutment shoulders 126 than it is at the aperture 121. In other words, the outer channel 124 tapers outwardly as it approaches the longitudinal axis of the cavity forming device 100. In this embodiment, the taper is approximately 10 degrees although an alternative taper of between about 5 and 15 degrees would be useful.

The combination of a deeper outer channel 124, and in particular abutment shoulders 126, and tapering outer channel 124 allows the cavity forming device 100 to be attached to a timber frame wall tie 150 in a way different to that described with reference to the first exemplary embodiment. Here, the cavity forming device 100 is flipped over when used on a timber frame cavity wall 160. The cavity forming device 100 of the second exemplary embodiment is fed over the timber frame wall tie 150 so that the second face 120 abuts the plywood covering 163 of the inner skin 161. The timber frame wall tie 150 is fed into the tapering outer channel so that the aperture 121 of the outer channel 124 is facing substantially up. The tapered walls of the outer channel 124 act to prevent the cavity forming device 100 from slipping down against the inner skin 161. The angled and deeper abutment shoulders 126 provide a good contact with the timber frame wall tie 150 and the cavity forming device 100 is frictionally held in place against the inner skin 161.

FIG. 8 is a side view of a timber-clad cavity wall having the cavity forming device of FIG. 5 installed therein.

As can be seen, the cavity forming device 100 has been flipped over when compared with the equivalent installation in FIG. 3 of the first exemplary embodiment.

The slot 138 on the first exemplary embodiment is therefore redundant and has been removed from the cavity forming device 100 of the second exemplary embodiment.

Finally, the rim 114 of the first face has been widened in the second exemplary embodiment to better support the lugs and to provide better contact.

With reference to FIG. 5, a method of constructing cavity walls is now described.

The method comprises building an inner skin 161 to a predetermined height including attaching at least one wall tie 150, 152. Then, the cavity forming device 100 is held against the inner skin 161 so that the cavity forming device 100 receives the wall tie 150, 152. The backing board 165 is then positioned against the cavity forming device 100, in particular the second face 120, and the backing board 165 is secured against the second face 120 using the wall tie 150, 152 and optionally a wall tie retaining clip 168.

Then, the method comprises building an outer skin 164 to a predetermined height adjacent the backing board 165 and using the wall tie 150, 152 to secure the outer skin 161 to the inner skin 164.

As will be apparent to the reader, the inner skin may be built of concrete block work, brick work or other masonry, or may be timber-clad.

Where a general purpose wall tie 152 may be used between courses of masonry, for example, then the cavity forming device is secured in place by attachment to the general purpose wall tie 152 using the notch 122.

Where the inner skin is timber-clad, the timber frame wall tie 150 and cavity forming device 100 are both secured to the timber cladding by a brad nail 151, or other suitable fastening such as a screw.

The inventor has also found that a backing board 165 may advantageously be sheets of corrugated polypropylene board 165. Preferably, the corrugated polypropylene board 165 is pre-cut to correspond to the height between two-courses of block work so that no further trimming of the corrugated polypropylene board 165 is necessary. One suitable backing board is 8 mm thick, but any thickness between 2 mm and 25 mm is envisaged.

The cavity forming device 100 may be made from any suitable material, such as a plastics material. The size and configuration of the cavity forming device 100 may be modified to suit the cavity wall in which the cavity forming device 100 is to be installed.

The cavity forming device 100 has three ribs 132, but any other suitable number ribs could be employed.

The cavity forming device 100 sets a distance of 50 mm between the first face 110 and the second face 120. However, other distances are envisaged. For example from 25 mm to 200 mm. More commonly 100 mm.

The cavity forming device 100 suitable for both masonry cavity walls and timber-clad cavity walls has been shown and described. Of course, the skilled person would realise that a specialist cavity forming device 100 suitable only for masonry cavity walls on one hand, or timber-clad timber walls on the other hand, could be used. For example, a cavity forming device 100 to be used solely with timber-clad walls need not comprise the inner channel 125 and detent notch 122. Conversely, if the cavity forming device is for use only with masonry cavity walls, then the lugs 112 and lug apertures 113 could be removed. Additionally, the outer slot 124 could be removed. The inner slot 125 could, optionally, extend to the outer circumference of the second face 120. Of course, this is not essential as the cavity forming device 100 could be placed over a general purpose wall tie 152 in use, or a timber clad wall tie 150, so that the wall tie pushes through the second face.

Traditionally, wall ties are inserted every two courses of concrete block work, or natural stone work. The cavity forming device 100, method and cavity wall, together with the backing board described herein have this method of construction in mind. However, wall ties could be spaced at any distance on a cavity wall and the above invention could be utilised.

Although a few preferred embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. 

1. A cavity forming for a cavity wall, the device comprising: a first face; a second face connected to the first face by the body to set a predetermined distance between the first face and the second face corresponding to a cavity depth in use; and wherein the second face is arranged to receive a wall tie therethrough.
 2. The cavity forming device of claim 1, wherein the device has means for securing the cavity forming device within the cavity wall.
 3. The cavity forming device of claim 2, wherein the means for securing allows the cavity forming device to attach to a wall tie.
 4. The cavity forming device of claim 3, wherein the means for securing is a detent notch for attachment to the wall tie, wherein the detent notch is located on the second face.
 5. The cavity forming device of claim 1, wherein the cavity forming device comprises a channel with abutment shoulders for attaching the device to the wall tie.
 6. The cavity forming device of claim 1, wherein in which the cavity forming device has a lug defining an aperture which is arranged adjacent the first face.
 7. The cavity forming device of claim 1, wherein the first forms a generally horse-shoe type circumferential rim defining an opening.
 8. The cavity forming device of claim 1, wherein the body is generally cylindrical and comprises a plurality of ribs.
 9. The cavity forming device of claim 8, wherein the ribs include bowed mid sections to prevent moisture travelling along the ribs.
 10. The cavity forming device of claim 1, wherein the body comprises a slot adjacent the first face.
 11. A method of constructing a cavity wall, the method comprising: a) building an inner skin to a predetermined height including attaching at least one wall tie; b) securing a cavity forming device against the inner skin so that the cavity forming device receives the wall tie; c) positioning an outer skin backing board against the cavity forming device; d) securing the backing board against the cavity forming device using the wall tie; e) building an outer skin to a predetermined height adjacent the backing board using the wall tie to secure the outer skin to the inner skin.
 12. The method of claim 11, wherein the cavity forming device is secured against the inner skin using the wall tie.
 13. The method of claim 11, wherein the backing board is secured against the cavity forming device using a wall tie retaining clip.
 14. A cavity wall comprising: an inner skin including at least one wall tie; a cavity forming device arranged against the inner skin so that the cavity forming device receives the wall tie; an outer skin backing board held against the cavity forming device; a wall tie retaining clip attached to the wall tie to hold the backing board against the cavity forming device; and an outer skin adjacent the outer skin backing board.
 15. The cavity wall of claim 14 wherein the backing board is corrugated polypropylene board. 